Free piston engine hydraulic pump starting system



4 Sheets-Shee t 1 E. A. KARIBA ETAL Nov. 10, 1964 FREE PISTON ENGINE HYDRAULIC PUMP STARTING SYSTEM Original Filed Aug. 17, 1961 Nbv- 1964 I E. A. KARIBA ETAL FREE PISTON ENGINE HYDRAULIC PUMP STARTING SYSTEM 4 Sheets-Sheet 3 Original Filed Aug. 17, 1961 Nov. 10, 1964 E. A. KARIBA ETAL FREE PISTON ENGINE HYDRAULIC PUMP STARTING SYSTEM Original Filed Aug. 1'7, 1961 4 Sheets-Sheet 4 United States Patent Office as ist Patented Nov. 10, 1964 3,156,088 FREE PTSTGN ENGHNE HYBRAULEC PUMP STARTING SYSTEM Edwin A. Kariha, tChicago, and C Paul Kolthoil, .ln, Naperville, ill, assignors to international Harvester (Iompany, Chicago, Tih, a corporation oi New Jersey Griginal application Aug. 17, 1961, Ser. No. l32,tl39. Divided and this application June 4, 1962, Ser. No.

3 Claims. (Cl. till-14) This case is a division of application Ser. No. 132,089, filed August 17, 1961.

This invention relates to a single cylinder free piston engine wherein the reaction of the piston moving in one direction is compensated by movement of the engine block in the other direction in balanced relation thereby minimizing or eliminating vibratory forces on the engine support. More in particular this invention relates to a dynamically balanced single cylinder free piston engine having minimal vibratory stress on the support means therefor. In the past, single cylinder reciprocating piston internal combustion engines of the free piston type have their blocks supported in stationary relation. Thus reactive forces occurring during piston movement must be absorbed by the engine and its support which necessitated strong mounting means to accommodate these vibratory shock forces. The present invention contemplates overcoming this problem by providing a movable engine block which always moves in a direction opposite to the movement of the piston. Now if the eiicctive mass of the engine block is substantially equal to the effective mass of the piston then a full stroke of the piston relative to the block actually moves only one-half of a full stroke with respect to the stationary engine mounting, the other one-half stroke being the movement of the block in the opposite direction.

The term effective mass as employed herein is intended to mean the total weight including all components which reciprocate together including an amount to compensate for friction.

The utility or" the engine of this invention may be that Of a gasifier for driving a turbine. However, this invention also contemplates deriving work from the engine by incorporating a fluid pump, such as a hydraulic pump, within the engine structure.

It is therefore a prime object of this invention to provide a single cylinder free piston engine wherein the engine block moves in one direction substantially equal to the distance the piston moves in the other direction.

Another object of this invention is to provide a single cylinder free piston engine wherein the support means for the engine is substantially free from vibrating stresses during operation.

Still another object of this invention is to provide a free piston according to the proceding obiects wherein the engine has an internally constructed fluid pump.

Yet another obiect of this invention is to provide a starting means for the free piston engine according to the preceding objects.

These and other important objects inherent in and encompassed by the invention will be more readily understood from the ensuing description, the appended claims and the annexed drawings wherein:

FiGURE 1 is a vertical cross-section view taken along the longitudinal axis of the free piston engine pump of this invention.

FIGURE 2 is a transverse cross-section view taken along the line 2-2 of FIGURE 1 illustrating the arrangement of the check valves for the engines air compressor.

FIGURE 3 is a transverse cross-section View with power piston and head removed taken along the line 3-3 of FIGURE 1 showing a portion of the engine block with its cylinder sleeve or liner.

FIGURE 4 is a transverse cross-section view, taken on line d l of FIGURE 1, illustrating the stationary fluid pump cylinder with pump pistons removed.

FIGURE 5 is a transverse cross-section view, taken on line 55 of FIGURE 1, showing the connecting means between the movable engine block and its associated fluid pump piston.

FIGURE 6 is a modification of the fluid pump, shown schematically, which provides automatic correction for any creeping of the stroke center point.

FIGURE 7 illustrates, schematically, an hydraulic starting system for the free piston engine pump of this invention.

With continued reference to the drawings in FIGURE 1 the numeral Ill indicates generally the free piston engine fluid pump of this invention. The engine It) comprises a lock member which for manufacturing and assembling reasons comprises a cylinder head 11, an upper casing 12 anda lower casing 13 rigidly connected together as by bolts, three of which are shown at 14, 15 and 16. The block member ill, 12 and 13, is preferably made of a low specific gravity material such as, for example, aluminum alloy.

The block member 11, 12 and 13, is provided with conventional fins 17 to facilitate disposition of heat which avoids the necessity of increasing its mass by providing a conventional liquid coolant jacket.

The block member 11, 12 and 13 may be provided with a conventional wear resistant sleeve or cylinder liner 18 to faci itate slidable movement of a power piston assembly generally indicated at T9. i

The engine it) is provided with a combustion chamber 25?, an air compressor chamber 21 and a resilient reaction chamber 22 commonly referred to as the bounce cham her. The power piston 19 includes, as a portion thereof, a large piston or compressor piston 23. The bounce chamber 22 of this device operates for only a portion of the compressor piston stroke as it is vented to the atmosphere when the compressor piston 23 uncovers the port 22. in the lower casing 13. This provides an initial atmospheric bounce pressure for each operating cycle. if the port 22' was omitted, the initial bounce pressure could fluctuate, depending on leakage from or to the bounce chamber 22. The block member l1, l2 and 13 is provided with at least one air inlet check valve 24 and at least one air outlet check valve 25. The check valve 24 permits air to enter from the atmosphere (or external supercharger) into the compressor chamber 21 during the intake stroke of the compressor piston 23. The checlt valve 25 permits air from the compressor chamber 21 to discharge under pressure into the air box 26 during the compression stroke of the compressor piston 23. Air inlet ports 27 communicate compressed air from the air box 25 into the combustion chamber Zll through the cylinder liner it; as shown in FIGURES 1 and 3. Exhaust ports 28 are also provided for discharging the products of combustion from the chamber 20 through the cylinder liner 1% and upper casing 12; into conduit 29 as shown. The ports 27 and 23 are valved by movement of the power piston 19 as is conventional in loop scavenged two-cycle engines.

Referring now to FIGURES 1 and 2 it will be seen that the air check valves 24- and 25 as shown comprises a plurality of conventional reed type valves. Thus as shown a total of twenty-four reed valves comprise the air inlet check valve 24 and an equal number comprise the air outlet check valve 25. Reed type valves are preferable as they are of low mass and quite sensitive to a reversal of diiierential pressure of low magnitude.

The cylinder head 11 is provided with a conventionalaneepse fuel injector, indicated at 30, which injects a metered quantity (selectively variable) of fuel into the combustion chamber when the pressure in the chamber 20 elevates beyond a predetermined value. Subsequently when the pressure in chamber 20 is reduced below a predetermined pressure the fuel injector automatically resets itself preparatory to the next fuel injection cycle. Numerous types of fuel injecting mechanisms of this type are known, one of which is described in US. Patent No. 2,799,263 to Louis 0. French.

Slidably disposed in the cylinder liner 18 is the power piston 19 which may be provided with conventional sealing rings, three of which are shown at 31. Likewise the compressor piston 23 portion of the power piston as sembly 19 may also be provided with conventional sealing rings three of which are shown at 32. As indicated the compressor piston 23 is in slidable relation with an internal bore 33 disposed within the lower casing 13 of the block member.

Rigidly secured in stationary relation is a support member, generally indicated at 34, for the engine It The support member 34 may conveniently be secured to a rigid foundation, a fragmentary portion indicated at 35 in FIGURE 1, as by bolts, two of which are shown at 36 and 37. The support member 34 comprises a base plate 38 rigidly connected to a stationary fluid pump cylinder 39 extending perpendicularly therefrom as shown in FIGURE 1.

Referring to FIGURE 5 it will be seen that the pump cylinder 39 is provided with an elongated slot 40 extending longitudinally a distance somewhat greater than onehalf the maximum stroke of the power piston 19 relative to the block member 11, 12 and 13. The longitudinally extending sides of the slot 40 are defined by the walls 41 and 42 as best shown in FIGURE 5.

Disposed in longitudinally movable relation within the slot 40 in the pump cylinder 39 is a transverse bracket 43 the end portions of which are secured to the lower end of the block member as by bolts 44 and 45. Thus as the lower casing 13 of the block member reciprocates in slidable relation with the outer surface 46 of the pump cylinder 39, the bracket 43 reciprocates in the slot 40.

Connected in longitudinal drive relation to the bracket 43 is a lower pump piston 47. The pump piston 47 is in slidable relation within a longitudinally extending bore 48 disposed within the stationary pump cylinder 39 as best shown in FIGURE 1. The pump piston 47 is connected to the bracket 43 by a conventional ball and socket linkage, generally indicated at 49, which compensates for any misalignment between the bore 48 and the outer surface 46 of the fluid pump cylinder 39 due to manufacturing tolerances. Thus it can be seen that the lower pump piston 47 moves reciprocatingly with the block members 11, 12 and 13.

Within the bore 48 of the pump cylinder 39 in opposed relation with the lower pump piston 47 is an upper pump piston 50 connected to the power piston assembly 19 for longitudinal movement therewith. The power piston assembly 19 includes a bracket 51 connected to the piston 19 as by bolts, two of which are shown at 52 and 53. The connection between the bracket 51 and the upper pump piston 50 is by means of a conventional ball and socket linkage indicated at 54 which allows some transverse movement of the pump piston 50 with respect to the power piston 19. This prevents binding of the pump piston 50 with the bore 48 by reason of slight misalignment due to manufacturing tolerances. Thus the upper pump piston 50 reciprocates with and is part of the power piston assembly 19.

The pump cylinder 39 is provided with a longitudinal bore 119 shown in dotted lines in FIGURE 1 is provided for venting to the atmosphere the space 120 so that it does not function as an auxiliary bounce chamber which otherwise might create unwanted forces. Further it serves to assist in cooling the underside of the piston 19.

Between the inner face 55 of the upper pump piston 55) and the inner face 56 of the lower pump piston 47 in the bore 48 is a fluid pump chamber 57. Referring now to FIGURES 1, 4 and 5 it will be seen that the stationary fluid pump cylinder 39 is provided with two longitudinal fluid conducting bores, one being a fluid inlet bore 58 and the other being a fluid outlet bore 59, both bores being in parallel spaced relation and extending through the base plate 38. The inlet bore 58 is connected to a source of low pressure fluid such as a reservoir or accumulator 6-9 through a conventional inlet check valve 61 as indicated in FIGURE 7. Similarly the outlet bore 59 communicates with a high pressure accumulator or other fluid pressure receiving device 62 through an outlet check valve 63 indicated also in FIGURE 7.

Referring to FIGURE 4 it will be seen that the fluid inlet bore 58 communicates with the pump chamber 57 through transverse bore 58 and the fluid outlet bore 59 communicates with the pump chamber 57 through transverse bore 59 as shown.

Although the engine pump 10 is capable of being started by conventional means a novel starting system particularly adapted for the engine pump 10 is shown schematically in FIGURE 7.

Referring to FIGURE 7 the letter M represents an hydraulic motor preferably of the rotatable type such as a gear motor. The hydraulic motor M drives an hydraulic pump P, preferably of the rotatable type such as a gear pump, mechanically through linkage indicated at 64. Thus when the motor M is energized it drives the pump P mechanically.

The numeral 65 indicates a fluid metering unit comprising a metering cylinder 66 having a metering piston 67 slidably disposed therein. The volume below the piston 67 is termed the metering chamber 68 and the volume above the piston 67 is termed the actuating chamber 69. When the piston 67 is in the position shown in full lines the actuating chamber 69 is of large volume while that of the metering chamber 68 is approaching zero. On the other hand when the position of piston 67 is in the position 67 as shown in dotted lines the reverse is true.

The starting system is provided with a fluid sump 70 and a start valve indicated at 71. The start valve 71 is a spool type valve comprising a housing 72 having a bore 73 therein. Slidably disposed within the bore 73 is a spool valve member indicated at 74. The valve member or plunger 74 comprises a pair of lands 75 and 76 separated longitudinally by a circumferential groove 77. The land 75 is positioned in registerable relation with port 78 and land 76 is positioned in registerable relation with port 79. A third port 80 is positioned for registration with circumferential groove 77. A compression spring 81 is positioned as shown for urging the plunger 74 rightwardly toward the position indicated in dotted lines. Within the bore '73 rightwardly of the plunger 74 is a valve chamber 82 in communication with conduit 83 through connecting conduit 84. Thus when the valve chamber 82 is energized the plunger '74 moves leftwardly to the position shown in full lines and when the chamber 82 is (lo-energized the plunger 74 moves rightwardly to the position shown in dotted lines due to the action of spring 81.

The outlet side of the hydraulic motor M communicates with the sump 7!) through conduits 65 and 86 while the dlscharge side of pump P communicates with the sump 70 through conduits and 87 as shown. The inlet side of pump P communicates with the pump chamber 57 of the engine 19 through conduits 88, normally closed manually operated valve 101 and conduit 59'. A vacuum limiting bypass for conduit 88 is provided for the pump P through conduit 39 and relief valve 90 as indicated. The inlet side of the motor M communicates with the actuating chamber 69 of the metering unit 65 through conduits 91 and 92. A normally closed manually operated valve 93 is interposed in the conduit 91 as shown.

The actuating chamber 69 of the metering unit 65 comvtions.

municates with the high pressure fluid accumulator 62 through conduits 92 and 94. A normally open manually operated valve 95 is interposed in the conduit 92 as indicated. Interposed in the conduit 94 to 94 as shown is a normally closed manually operated valve 96.

The conduit 94 also communicates with the metering chamber 68 of the metering unit 65 through conduits 97 Operation When the engine pump id is shut down after operation it can readily be appreciated that the fluid pump pistons 47 and 50 may come to rest at most any position of their respective strokes. The starting system requires that the pump pistons 47 and Si must first be brought to their maximum inboard position as illustrated in FIGURE 1. Thereafter a metered charge of high pressure hydraulic fluid is introduced into the pump chamber 57 which drives the pump pistons 47 and 5d outwardly in opposite direc- This has the effect of driving the power piston 19 on its fuel-air compression stroke with respect to the movable block member 11, 12 and 13. As soon as the compression pressure in the combustion chamber 2% rises to a predetermined value, the pressure actuat es the fuel injector 39 whereby a metered charge of fuel is injected into the combustion chamber 2%. Compression in the combustion chamber 2-9 continues to rise at the urging of the initially created inertia of movement even without further urging of fluid pressure in the pump chamber 57 until combustion occurs through compression-ignition. The power piston 19 thereafter is driven downwardly and the reaction force against the head 11 drives the block member 11, 12 and 13 upwardly. However since the effective mass of the power piston assembly 11% including its associated members aggregately is substantially equal to the effective mass of the block member Ill, 12 and 13 including its associated elements, the distance that the power piston 19 moves downwardly with respect to the stationary support member 34 will be substantially equal to the distance the block member 11, 12 and 13 moves upwardly. The power stroke thus compresses the air in the bounce chamber 22 which reacts to move the power piston 1t? and the block member in the opposite direction thereby initiating the next compressionignition cycle. On succeeding cycles there is no metered charge of high pressure hydraulic fluid for then the pump chamber 57 is filled by low pressure oil from accumulator 66.

Starting Referring to FIGURE 7 the high pressure fluid accumulator 62 must be charged under pressure. Assuming no fluid leakage the accumulator 62 will be charged from the previous operation of the engine pump it Otherwise the accumulator 52 must first be charged from an external source.

Step 1.Close all normally open valves. words close valves 95 and 1th).

Step 2.-Open normally closed valves )3, N1 and 71'. This permitshydraulic'fluid in valve chamber 82 to escape through port 80 and conduit 99 so that spool valve member 74 may move to the position indicated by the dotted lines as urged by the spring 81.

Step 3.Close the start control valve 71.

Step 4.-Open the normally closed valve 96. This permits the fluid pressure from the high pressure accumulator 62 to pass through conduit 94, open valve 96,

In other conduit 94', conduits '97 and 98 to pressurize metering chamber 63 of the fluid metering unit 65. Pressurizing the metering chamber 68 now urges the metering piston 67 upwardly thereby also pressurizing the actuating chamber 69. Pressurizing the actuating chamber 69 discharges the fluid therein through conduit 92, opened valve 93 and conduit 91 to the inlet side of motor M. The discharge from the motor M passes to the sump through conduits as and $5. The hydraulic motor M is thus energized to drive the pump P in a direction for evacuation of fluid from the pump chamber 57 of the engine .pump Ifl. It will be noted that the valve is closed during this step so that the metering piston 67 will be urged upwardly to the position shown at 67. Since the pump P is still being driven by the motor M and the valve is closed the pump chamber57 of the engine pump 10 will be under sub-atmospheric pressure which draws pump pistons 47 and 5% toward their respective inboard positions and the evacuated fluid from the pump chamber 57 is delivered to the sump 70 through conduits -59, opened valve ltlll, conduit 88, pump P, and conduits 8.7 and 85. When the pump pistons 47 and 50 have reached their respective inboard positions as shown in FIGURE 1, and the metering piston 67 has been elevated to its upper limit the system is ready for the next step. An inlet check valve 118 manually openable for reverse fluid flow is provided on the lower casing 13 of the block member to exhaust the bounce chamber for facilitating inboard movement of the power piston with respect to the block member.

Step 5.-Close all of the previously opened normally closed valves. In other words close valves 93, 96 and 101. This step has the effect of terminating further discharge from the high pressure accumulator 62. and thus the hydraulic motor M becomes de-energized thereby terminating operation of the pump P. However the metering piston 67 will remain elevated because the spool valve member 74 will still remain in its rightward position, shown in dotted lines in FIGURE 7, and valves 71' and as are in closed position. Thus fluid in the metering chamber 68 is under fluid lock.

Step 6.Open all of the previously closed normally open valves. In other words open valves 95 and 100. Opening of the valve 95 has no effect except to pressurize the actuating chamber 69 which of course urges the metering piston 67 downwardly. However, the metering piston 67 does not move downwardly because the fluid in the metering chamber 68 is under hydraulic look as previously explained but of course the fluid in chamber 63 is now pressurized. Opening of the valve 100 has no eflect during this operation.

Step 7.Open the start control valve 71'. Opening of the start control valve 71' the valve chamber 82 is pressurized through conduits 83 and 84 from the high pressure accumulator 62 which shifts the spool valve member 74- to the position shown in full lines in FIG- URE 7. As soon as port 8% is uncovered the valve chamber 82 is pressurized from port 79. Fluid under pressure in the metering chamber 68 is now in communication with the pump chamber 57 of the engine pump 10 by way of conduit 98, port 79, circumferential groove 77, port 78, conduits 99, 59 and 59'. Fluid pressure from the accumulator 62 in the actuating chamber 69 now urges the metering piston 67 from its position 67' to the position shown in full lines in FIGURE 7. The fluid in the metering chamber 68 between the position of the metering piston at 67 to that at 67 is a metered quantity for when the piston 67 has reached its lower limit no further fluid flow is delivered to the pump chamber 57. Thus the volume displacement of the metering chamber 68 should be approximately equal to the displacement of the pump pistons 47 and 50 so that a single charge of fluid from the metering chamber 68 is suflicient to move the power piston 19 and block members 11, 12 and 13, through the fuel-air compression stroke and compression-ignition thereof. The engine pump 10 thereby makes its initial firing and thus it continues to operate.

After the engine pump 10 is started it is immaterial whether the spool valve 71 is de-energized. However, as a practical matter the start valve '71 becomes de-energized because when the pump pistons 47 and 50 are moving outboardly (intake stroke) there is a momentary period of low pressure in the conduit 59 which is in communica tion with the valve chamber 82. This permits the plunger 74 to move rightwardly as viewed in FIGURE 7 and thus the port 78 is closed by the land provided however that the manually operated start control valve 71' is first closed.

The engine pump 10 is thus running and pumps fluid from the low pressure accumulator 60 to the high pressure accumulator 62. Since a differential fluid pressure exists between the high pressure accumulator 62 and the low pressure accumulator 60, this differential fluid pressure is available for performing useful work such as energizing fluid motors for driving machinery and the like. The fluid pressure in the low pressure accumulator 66 should be sufliciently high to prevent cavitation of fluid in the pump chamber 57 at higher engine speeds.

It will be noted that if the effective mass of the block member and its associated pump piston is equal to the effective mass of the power piston assembly with its associated pump piston, the stroke distance of each relative to the support member 34 will be equal and in opposite direction due to the opposed force reactive relation between the two. Thus no vibrational forces are imparted to the support member 34. In order to balance the respcctive effective masses, the block member should be made of low density material such as aluminum alloy (except for liner 18) while the power piston assembly should be made of higher density material such as iron or steel.

In the operation of the engine pump It above described the median of the fluid pump chamber 57 indicated by the line 1G2 (FIGURE l) may tend to creep in a longitudinal direction with respect to the support member 34- due to uneven wear or differences in manufacturing tolerances. In order to maintain the center of the fluid pump chamber 57 on the line 1512 so that neither the power piston 19 nor the block members 11, 12 and I3 reach their stroke limiting means with respect to the support means 34, a novel arrangement is shown in FIGURE 6 for accomplishing this purpose.

Referring to FIGURE 6 the fluid pump chamber 57 of FIGURE 1 is divided into two chambers, an upper pump chamber 103 and a lower pump chamber 104 separated by the wall 105 of the fluid pump cylinder 39. Thus the bore 48 of FIGURE 1 is divided into two longitudinal coaxial bores 1% and 197. The upper pump piston 5% is provided with a frusto-conical portion and the lower pump piston 47' is provided with a frusto-conical portion 109, both being on the inner ends of their respective pump pistons as shown in FIGURE 6. The fluid inlet to the lower pump chamber 164 is provided by the transverse primary inlet bore 1.16 communicating with the inlet bore 58. Likewise the fluid inlet to the upper pump chamber 103 is provided by the transverse primary inlet bore 111 also communicating with the inlet bore 53 as shown.

In the same transverse plane as that of the bore 111 is a bore 112 which communicates the upper pump chamber 103 with the fluid outlet bore 59. Likewise, in the same transverse plane as that of the bore I10 is a bore 113 which communicates the lower pump chamber 164 with the fluid outlet bore 59. At this point it will be observed from FIGURE 6 that the longitudinal distance between bores 111 and 112 from the wall 105 is equal to the longitudinal distance between the bores 11% and 113 and the wall 105.

The upper pump chamber 103 is also provided with a secondary fluid inlet passage 114, communicating with inlet bore 58, having a conventional check valve 115 interposed therein as shown in FIGURE 6. Similarly the lower pump chamber 164 is provided with a secondary fluid inlet passage 116, communicating with inlet bore 53, having a conventional check valve 117 interposed therein. It will be noted that the secondary inlet passages 114 and 115 are positioned adjacent to the wall 105 as illustrated in FIGURE 6.

Again referring to FIGURE 6, during operation of the engine pump 10 if the inbound movement of the lower pump piston 47 becomes excessive due to a shift of the piston and block assemblies to the left for some reason as indicated by the dotted lines, the pump piston 47 progressively throttles fluid flow in the bores and 113. This results in a progressive increase in fluid pressure in the lower pump chamber 104 which in turn increases the resistance to movement of the lower pump piston 47' associated with the block members 11, 12 and 13. Now if the upper pump piston 50' is always the same distance from the wall 135 as that of the lower pump piston 47', then the fluid pressures in both chambers 163 and 10-1- will be equal to each other at all times. However in the event that the respective distances of the pump pistons 47 and 53 become unequal with respect to the wall 105 then the fluid pressures in the chambers 103 and 104 will become unequal. Since the force driving piston 47' is reactive with the force driving the piston 59 the pump chamber having the higher pressure will cause the other piston to increase its stroke. For example, as shown in FIGURE 6, if the pump piston 47 moves on its inbound stroke toward the position shown in dotted lines, the pressure in the chamber 104 progressively rises. This progressive rise in pressure in chamber 104 also progressively increases the resistance to further inbound movement of the pump piston 47. The progressively increasing resistance to inbound movement of pump piston 47 reflects to increase the inbound force of the pump piston 50' as the forces driving pistons 47' and 50 are reactive as previously explained. The increased inbound force thus applied to the piston 56 tends to raise the pressure in chamber 193 to equal that in the chamber 104. However, there is no substantial increase in pressure in the chamber 193 until the piston 5% begins to register with the bore 11.4.1 whereby fiuid flow thcrethrough becomes restricted. From this it is evident that progressive restriction of flow through bore 112 correspondingly increases the pressure in chamber 103 until it is equal to the pressure in chamber 1'94- at which time the piston 59' will be substantially at the same distance from the wall 105 as that of piston 47'. Thus the midpoint between the pistons 47' and 50 will always coincide approximately with the center of the wall 105.

During the outbound movement of the pistons 47 and 56 the check valves and 117 in the secondary passages 114 and 116 open to permit free access of fluid into the chambers 1&3 and 105 without restriction irrespective of the positions of the pistons 47 and 59. Thus any tendency for the midpoint between the pistons 47 and 50 to shift or creep longitudinally is automatically corrected in the arrangement shown in FIGURE 6.

Having thus described a preferred embodiment of the invention it can now be seen that the objects of the invention have been fully achieved and it must be understood that changes and modifications may be made which do not depart from the spirit of the invention nor from the scope thereof as defined in the appended claims.

What is claimed is:

l. A starting system for a free piston engine hydraulic pump having a power piston connected to a pump piston and at least one pump chamber comprising, in combination, a fluid metering unit communicatively connectable to a source of hydraulic fluid at high pressure, means for moving said power piston of said engine into initial position of fuel-air compression stroke, valve means positioned to communicate said metering unit with said source for hydraulically charging said unit under high pressure, and a start valve positioned to discharge hydraulic fluid rapidly 'from said charged metering unit to said pump chamber whereby said pump piston drives said power piston on its initial fuel-air compression stroke until compression-ignition occurs thereby starting said engine.

2. A starting system for a free piston engine hydraulic pump having a power piston connected to a pump piston and at least one pump chamber comprising, in combination, a fluid metering unit connectable to a source of hydraulic fluid under high pressure, said metering unit being capable of discharging upon actuation a predetermined amount of hydraulic fluid at high pressure, means for moving said power piston of said engine into initial position of fuel-air compression stroke, first conduit means positioned for communicating said source with said metering unit to charge said unit under pressure, first valve means interposed in said first conduit means openable for charging said metering unit from said source, second conduit means positioned for communicating said charged metering unit with said pump chamber of said engine, and a start valve interposed in said second conduit means openable to discharge hydraulic fluid rapidly from said charged metering unit to said pump chamber whereby said pump piston drives said power piston on its initial f relair compression stroke until compression-ignition occurs thereby starting said engine.

3. A starting system for a free piston engine hydraulic fluid pump of the kind described having a pair of opposed pump pistons and at least one pump chamber comprising a chargeable fluid metering unit communicatively connectable to a source of hydraulic fluid at high pressure, said metering unit having a fluid volume capacity substantially equal to the maximum displacement of said pump pistons, an auxiliary hydraulic pump driven by an hydraulic motor energizable from said high pressure source, the inlet side of said auxiliary pump communicatively connectable to said pump chamber for fluid evacuation of said chamber to move said pump pistons inboardly by atmospheric pressure to initial compression stroke position, and a start valve positioned for rapidly discharging hydraulic fluid from said metering unit at high pressure to said pump chamber for moving said pump pistons outboardly whereby at least one of said pump pistons drives said power piston on its initial fuel-air compression stroke until compression-ignition occurs thereby starting said engine.

References Cited in the file of this patent UNITED STATES PATENTS 2,914,909 Kubik Dec. 1, 1959 2,978,986 Carder et a1. Apr. 11, 1961 3,031,972 Janicke May 1, 1962 

3. A STARTING SYSTEM FOR A FREE PISTON ENGINE HYDRAULIC FLUID PUMP OF THE KIND DESCRIBED HAVING A PAIR OF OPPOSED PUMP PISTONS AND AT LEAST ONE PUMP CHAMBER COMPRISING A CHARGEABLE FLUID METERING UNIT COMMUNICATIVELY CONNECTABLE TO A SOURCE OF HYDRAULIC FLUID AT HIGH PRESSURE, SAID METERING UNIT HAVING A FLUID VOLUME CAPACITY SUBSTANTIALLY EQUAL TO THE MAXIMUM DISPLACEMENT OF SAID PUMP PISTONS, AN AUXILIARY HYDRAULIC PUMP DRIVEN BY AN HYDRAULIC MOTOR ENERGIZABLE FROM SAID HIGH PRESSURE SOURCE, THE INLET SIDE OF SAID AUXILIARY PUMP COMMUNICATIVELY CONNECTABLE TO SAID PUMP CHAMBER FOR FLUID EVACUATION OF SAID CHAMBER TO MOVE SAID PUMP PISTONS INBOARDLY BY ATMOSPHERIC PRESSURE TO INITIAL COMPRESSION STROKE POSITION, AND A START VALVE POSITIONED FOR RAPIDLY DISCHARGING HYDRAULIC FLUID FROM SAID METERING UNIT AT HIGH PRESSURE TO SAID PUMP CHAMBER FOR MOVING SAID PUMP PISTONS OUTBOARDLY WHEREBY AT LEAST ONE OF SAID PUMP PISTONS 